1. Field of the Invention
The present invention relates to an electrostatic condenser type pressure sensor and a method for manufacturing the pressure sensor.
2. Background Art
In the related art, the electrostatic condenser type pressure sensor is constructed such that flat electrodes mounted on the individual confronting faces of two substrates are arranged to confront each other in parallel at a predetermined spacing. The pressure sensor is enabled to detect a pressure loaded from the outside, by detecting the change in the electrostatic capacity, as caused when one of the substrates is warped in the thickness direction by the external pressure.
Therefore, the spacing between the confronting electrodes has an extremely important meaning for uniformity for the detection accuracy. In JP-A-5-288623 or JP-A-10-111206, methods are disclosed using five ceramic and resin, respectively, beads to retain a predetermined electrode gap, for example.
However, either method uses the fine balls by mixing with a fluid adhesive. When the two substrates are made to confront each other and are integrally jointed so that the diameter of the fine balls may be the distance between the confronting substrates, therefore, the adhesive spreads, before solidified, more than necessary between the substrates. As a result, dispersion occurs in the fulcrum distance for supporting the diaphragms or substrates to be warped in the thickness direction by the external pressure. Thus, a problem arises in that the uniform detection accuracy is hardly obtained them the adjusting operation becomes complicated.
In JP-A-8-240500, on the other hand, there is disclosed a method for retaining a predetermined electrode gap by using a spacer having a discontinuous but uniform height in an electrostatic condenser type pressure sensor having a frit of a lower softening point than that of the spacer around the spacer.
As the external diameter of the substrates is made smaller, however, the pressure sensor has to arrange the frit near the discontinuous spacer, then the frit softened is allowed to invade through the spacer and is solidified. Therefore, dispersion also occurs in the fulcrum distance for supporting the diaphragms or substrates to be warped in the thickness direction by the external pressure. Thus, a problem arises in that the uniform detection accuracy is hardly obtained.